stable addressing

[Iljitsch van Beijnum <iljitsch@muada.com>]

As a result of discussions elsewhere, my concern about lack of stable 
addresses in IPv6 has increased once again. Let me first define four 
fairly typical classes of future IPv6 users:

1. single homed users
2. "basement multihomers": (very) small networks with two uplinks
3. content providers: lots of traffic, but not very many network 
components
4. enterprises: lots of subnets, lots of network components

If we consider NOID-like solutions with DNS names and PA addresses only 
and no longer-lived identifiers or addresses, this should work quite 
well for classes 1, 2 and 3, as the amount of equipment that must be 
reconfigured when a new ISP is connected is relatively small.

Things are different however for class 4. Here, renumbering is not a 
realistic option. Even if renumbering the actual network infrastructure 
were to be doable, changing the associated filters and related security 
setups is too much work to undertake at regular intervals.

So how do we solve this? I'm assuming NAT is not an option. One way 
would be to create address space that isn't regularly routable, but can 
be automatically tunneled/aliased over regular PA space. The 
disadvantage here is that tunnel/aliasing setup must happen prior to 
session establishement, which isn't all that great for incoming 
sessions towards these types of addresses, but presumably most sessions 
will either be outgoing or part of a longer-term meta-sessions so this 
shouldn't be as big a problem as with classes 2 and 3. Another problem 
here would be that even if the correspondent for the class 4 user 
doesn't actually multihome, they must still support the mechanisms in 
order to set up and use the tunnel. Again, this might be a disadvantage 
we're willing to swallow as the type of communication for class 4 is 
presumably limited to a subset of the full internet.

(Obviously an enterprise with lots of internal stuff but also highly 
visible stuff (think Cisco with their huge internal nework and also 
huge web presence) could use stable addressing for most of its network 
and PA/NOID for the most visible parts.)

Another side effect would be the need for a registry of some kind where 
the initial mapping information can be found in order to create 
tunneling/aliasing state.